Magnet control circuit



July 2, 1940. R. o. WERTZ MAGNET CONTROL CIRCUIT Filed Oct. 28, 1938 INVENTOR. 750) 0- WEETZ ATTORNEYS Patented July 2, 19433 UNi'l'ED STATES tATENT OFFiCE MAGNET CONTROL CIRCUIT Roy 0. hertz, Cleveland Heights, Ohio, assignor to @hio Electric Manufacturing 00., Cleveland, Qhio, a corporation of Ohio Application Dctober 28, 1938, Serial No. 237,445 4Claims. (Cl.175335) This invention relates to improvements in the main circuit caused an induced voltage to be electrical circuits, andmore particularly to imbuilt up in the magnet which sometimes got into provements in electro-rnagnet control circuits the main line and caused serious damage to oi the nature disclosed in my co-pending appliother apparatus operating from the main line.

cation for Magnet control, filed March 5, 1935, By my present invention I have provided a 5 Serial No. 10,243. circuit where the reversing is automatically ac- In the operation of electromagnets, and parcomplishecl, making only the on or lift and ticularh: those known as lifting magnets, it is the off or drop positions of the control nechighly desirable to provide a control circuit that essary- By this improved circuit there can be is partially automatic. Heretofore the magnet no quest-i01 of residual magnetism in the a 1 control master switch could be operated in two net which might hold the small bodies; and the positions besides the off position; that is the heretofore damaging inductive jump in voltage operator usually lowered the magnet onto or is not only k p Out Of the n e, but is used closely adjacent the material to be picked up, in the operation of the reversing control, and

d mgved th trol to the on or iii pothus substantially all of the deficiencies hereto- 15 to the mateii sition. This caused current to flow through the fore mentioned as existing in the prior devices windings of the magnet, causing the same to be are eliminated.

energized and attracting the magnetic material Still other advanta s o t e nvention and to the ma net. The magnet was then lifted and the invention itself will become ap from 211 conveyed to the position where it the following description of an embodiment therewas b dropped, When the operator Wanted of. Although I have described and illustrated to drop the material, he moved the control to the same as being applied to lifting magnets, the the reverse or drop position. This caused curnv n on m y l e pp ed o other yp s of rent to flow in a reverse direction through the electrc-magnets.

:5 windings and demagnetized the magnet, after The description is illustrated by the accomwhich the control was moved to the ofi po- D yin drawing whe e sition. It is with the de-magnetization of the Fig- 1 s a Schematic diagram of my improved magnet that this invention is particularly concircuit applied to a lifting magnet and showing cerned. The purpose of reversing the current t e in a lifting DOSitiOII- The o p t how was to reverse the polarity of the magnet 0f the circuit not in actual operation during the and thus dispose of any magnetic flux that might lift cycle are shown by dotted lines; remain therein from the lifting energizationj If Fig. 2 is a similar illustration showing the the control was merely moved to the off posicondition at the time of breaking the main cirtion from the lift position, small bodies of the w and nature of several pounds might adhere and drop Fig. 3 is a similar view showing the condition from magnet when being moved to a posiduring the reversing cycle. tion for another pick-up, endangering the lives Referring now to the drawing, the main line of the workmen in the vicinity. Reversing the from which power is obtained is indi t d t polarity, eliminated any possibility of such small the positive and negative signs and connected by bodies adhering to the magnet. This reversing conductors I to the Operating winding 2 o at operation was, however, endowed with several magnetically operated main circuit breaker. Indiihculties. In most instances the operator is terposed in one of the lines I is a remote control unable to see if the magnet has been freed of switch 3 which may b p ded With two selecits lead and it was only through long experience t Ve p t s; n 0105801 position indicated by that he attained sufiicient proficiency to deteron and an open position indicated by off. mine how long to hold the reversing circuit closed. The main circuit breaker contemplates: two main If he failed to hold the reversing circuit closed switch blades 4 for opening and closing the main long enough, he did not get rid of the magnetic circuit through the lines 5 and 6 to the winding flung if he held it too long, the polarity became l of the magnet M. When the main circuit 0 reversed and the magnet partially energized, and breaker is closed, current flows from. the positive he again re-picked up part of his load. side of the line through the conduit 5, blade 4, Still other disadvantages of the ordinary cirwinding 1, and blade 4, to the line 8, and thence cults included the damage caused by the inducis connected to the negative side of the main tive jump in voltage due to the breaking of the line. Closing the remote control switch closes high voltage circuit. The sudden breaking of the circuit breaker which is opened upon open- 55 ing the remote control switch by a spring l operatively connected to move the blades 4 when the winding 2 is de-energized.

The blades 4 are mechanically connected together as indicated at 8 and operate in unison. Also mechanically connected to the main circuit breaker blades 4 is a switch 9 that comprises a single blade which is so connected to the blades 4 of the main circuit that when the main circuit is closed the switch 9 is in the open position, and when the main circuit is open, the switch 9 is closed.

It is to be noted that current only flows in the main circuit in the direction of the arrows of Fig. 1 during the lift period, the remainder of the circuit shown by the dotted lines being inactive. When the main circuit breaker is opened, which is accomplished by moving the remote control switch to off, the winding 2 is de-energized and the spring ll) opens the main circuit; simultaneously the switch 9 is closed connecting a shunt circuit across the magnet.

The shunt circuit includes the switch 9 which is connected to a winding l! of a reversing relay I2. Connected in series with each other and in series with the winding II is a pair of resistances IS, the other end of said series connection being by the conductor I4 to the opposite or negative terminal of the magnet winding 1.

The shunt circuit being connected across the winding '1, simultaneously with the breaking of the main circuit, the induced voltage is circulated within the shunt circuit, the current flow being in the direction of the arrows; the resistances l3 serving to lower the current. This flow of current causes the winding H of the relay l2 to be energized attracting the armature l2 thereto, which armature is connected to the blade of the reversing switch l5, closing the reversing circuit.

The reversing circuit, controlled by the switch I5, is connected by the conductor E6 to the positive side of the main line. The switch i is connected by a conductor ll and a series resistance It to the conductor M which, as previously stated, was connected to the negative side of the magnet winding l. The current path is then, through magnet winding '1, switch 9, winding H, to the resistor iii in series with a conductor 2b which connects to a holding winding 2! of the relay I2. The other end of the winding 24 is connected by the conductor 22 to the negative side of the main line through the conductor 6.

When the reversing circuit is closed, the current flowing through the winding 2i polarizes the same and causes it to operate in conjunction with winding l! to hold the switch closed. In the meantime the inductive current in the shunt circuit gradually dies out because it is substantially a short circuit and because the current from the reversing circuit starts to oppose it. There comes a time, a matter of seconds or fractions of a second, when the winding ll is without current flow therein and only the magnetic flux in the winding 2i is holding the reversing switch [5 closed; at that time the current starts flowing in the reverse direction through the magnet winding 1, this fiow being indicated best by the arrows in Fig. 3.

It should be noted that as soon as the reverse current starts flowing overcoming the reactance of the magnet winding "l, the current flow starts in a reverse direction through the winding II to that of the flow immediately after the break. This causes the winding H to build up a polarity opposite to its original polarity and which opposes or bucks the polarity of the holding winding 2i. When the current flow in the reversing circuit reaches a predetermined amount, the winding H which is now a bucking winding, neutralizes the magnetic efiect of the winding 2|, and the spring 23 opens the switch l5 and the reversing circuit.

The resistances l8 and I9 serve to reduce the current in the reversing circuit.

The constants of the various windings and resistances are so proportioned that the reversing circuit is opened at the time when the reversing current demagnetizes the magnet M.

It will thus be seen that the de-magnetization of the magnet is completely beyond the control of the operator and is fully automatic. Not only is the inducted voltage disposed of, it is actually utilized to initiate the reversing circuit; and finally that the winding I I for the reversing circuit besides closing the reversing circuit is instrumental in opening the reversing circuit after a predetermined condition has been reached.

Although I have shown no manual reversing circuit, it may sometimes be advisable to provide such an auxiliary circuit, inwhich event the remote control switch would be provided with another position that would ordinarily be locked against use and would only be used for special applications.

Having thus described my invention in an embodiment thereof, I am aware that numerous and extensive departures will be apparent to those versed in the art, and it is not my intention that the invention be limited to the precise embodiment shown, otherwise than is claimed in the appended claims, and that the claims should be construed with a range of equivalents to which they may be entitled in view of the prior art.

I claim:

1. In a control circuit of the class described, a main circuit and a circuit breaker therefor for connecting a magnet to a current source, a reversing circuit connected to said current source and magnet for reversing current flow through the magnet, a shunt circuit and means for connecting said shunt circuit to said magnet upon the opening of the main circuit and means operable by current flow in the shunt circuit to close the reversing circuit and to open the reversing circuit upon a predetermined increase in current in the reversing circuit.

2. In a circuit breaker for an electro-magnet, a main circuit including a main circuit breaker connected to the magnet for controlling current flow from a current source to said magnet, means for counteracting the residual magnetism in said magnet upon the breaking of the main circuit including a secondary circuit therefor connecting the magnet and current source and adapted to reverse the current flow through the magnet, said secondary circuit including a starting circuit connected in shunt with the magnet for disposing of the induced high voltage caused by the breaking of the circuit and a circuit breaker actuated by current flow in the starting circuit to close said reversing circuit, said starting circuit acting in opposition to the reversing circuit to cause said relay to be released and open said reversing circuit upon a predetermined current flow in the reverse direction in said magnet.

3. In a control circuit for an electro-magnet,

a main circuit for connecting a current source to the magnet, a circuit breaker disposed in said circuit, means for disposing of the induced voltage upon breaking of the main circuit including an auxiliary circuit connected in shunt with the magnet, and a circuit breaker connected to said first circuit breaker adapted to close the auxiliary circuit upon opening of the main circuit, series resistance means in the auxiliary circuit for reducing the voltage therein, a reversing circuit for directing current flow from said source in a reverse direction through said magnet, means for connecting said reversing circuit to the magnet including a circuit breaker for controlling said reversing circuit and including an inductive winding for said circuit breaker connected in said auxiliary circuit adapted to actuate said circuit breaker to close said reversing circuit upon current flow through the auxiliary circuit, a second inductance winding for said circuit breaker disposed in series in the reversing circuit and adapted to hold said circuit breaker closed, said first mentioned winding means acting in opposition to said second winding means upon a predetermined reverse current flow to release said circut breaker and open said reversing circuit.

4. In a control circuit for an electro-magnet, a main circuit breaker for controlling current flow to the magnet from a current source, a reversing circuit for reversing the current flow from said source to the magnet to depolarize the same, a relay for controlling current flow in the reversing circuit and having windings, means todispose of the inductive voltage in said magnet upon breaking of the main circuit and to initiate the operation of the reversing circuit including an auxiliary circuit having a resistance and one of said relay windings connected in series to each other and connected in shunt with said magnet, said relay windings including a closing winding for operating the relay to close said circuit and a holding winding for holding said reversing circuit in electrical connection with said magnet, said closing winding of said relay operable by a predetermined increase of reversing current; through said magnet to release said relay and open said reversing circuit.

ROY O. WERTZ. 

